The present invention relates generally to underground drilling machines. More particularly, the present invention relates to a steerable fluid hammer apparatus for use in directional drilling.
Utility lines for water, electricity, gas, telephone, and cable television are often run underground for reasons of safety and aesthetics. Sometimes, the underground utilities can be buried in a trench that is subsequently back filled. However, trenching can be time consuming and can cause substantial damage to existing structures or roadways. Consequently, alternative techniques such as horizontal directional drilling (HDD) are becoming increasingly more popular.
A typical horizontal directional drilling machine includes a frame on which is mounted a drive mechanism that can be slidably moved along the longitudinal axis of the frame. The drive mechanism is adapted to rotate a drill string about its longitudinal axis. The drill string comprises a series of drill pipes threaded together. Sliding movement of the drive mechanism along the frame, in concert with the rotation of the drill string, causes the drill string to be longitudinally advanced into or withdrawn from the ground.
In a typical rotational directional drilling sequence, the horizontal directional drilling machine drills a hole into the ground at an oblique angle with respect to the ground surface. By rotating the drill string and drill head, dirt and stone is ground and cut into pieces. The cutting mechanism is the action of the drill bit being rotated and pushed against the rock and soil. To remove cuttings and dirt during drilling, drilling fluid can be pumped by a pump system through the drill string, over a drill head (e.g., a cutting or boring tool such as a drill bit) at the end of the drill string, and back up through the hole. After the drill head reaches a desired depth, the drill head is then directed along a substantially horizontal path to create a horizontal hole. Once the desired length of hole has been drilled, the drill head is then directed upwards to break through the ground surface, completing a pilot bore or bore-hole.
As an alternative to rotational drilling, impact cutting is employed to cut through especially hard substances like stone. Impact cutting involves the use of fluid pressure such as air or liquids to operate a fluid hammer. A fluid hammer includes a piston hammer which when activated by fluid pressure impacts repeatedly against the drill bit or a drill bit anvil, causing the cutting mechanism of the assembly to be a chipping or picking action rather than a grinding action. The drill bit used in impact drilling with a fluid hammer typically includes protrusions that function to reduce the effective surface area of the drill bit in contact with the rock.
In order to steer the apparatus during impact cutting, typically the drill bit is made unbalanced such that when not rotated it tends to deviate from a straight path and cuts in an arc. When drilling a curved bore the drill bit preferably is rocked so that the unbalanced protrusions on the drill bit eventually strike different portions of the rock face being drilled, gradually cutting an arced full bore. When a straight bore-hole is desired the drill bit is continuously rotated to prevent deviation from a straight path. Although effective, oscillating and rocking the drill string is a complicated, inefficient control technique. Furthermore, this method requires a more complex drill bit.
The present invention involves the use of a rotation means to rotate the fluid hammer and drill bit while the apparatus is being steered away from a straight path. By including in the drilling apparatus a means of rotation that may operate independently from the rotation of the drill string, a bent steering member may be held stationary by the drill string in order to steer the apparatus, while at the same time the fluid hammer and drill bit may be continuously rotated. Such an apparatus eliminates the need for complex drill bits. In addition, the method of operating and steering the apparatus is simplified by eliminating the need to rock the drill string.
One aspect of the present invention relates to a steerable directional drilling apparatus that includes a fluid hammer for impact cutting which is coupled to a bent steering member having a mud motor disposed therein. The mud motor is coupled to the fluid hammer such that the fluid hammer may be rotated even when the bent steering member is held stationary by a drill string. Thus, a balanced drill bit may be used with the fluid hammer which may be continuously rotated even when deviating from a straight path.
Another aspect of the present invention is directed towards a method for operating and steering a fluid hammer while drilling a bore-hole by coupling the fluid hammer to a bent steering member including a mud motor. In order to cut a straight bore-hole, pressurized fluid is supplied to activate the fluid hammer and the mud motor while the drill string is continuously rotated and advanced with limited force. The actual speed of rotation of the drill bit is the sum of the mud motor rotation and the drill string rotation. To deviate from a straight path, pressurized fluid is still supplied to activate the fluid hammer and the mud motor, but the drill string is held stationary to allow the bent steering member to force the apparatus to deviate. During deviation from a straight path, the fluid hammer and drill bit are rotated only at the speed supplied by the mud motor.
Another aspect of the present invention is directed towards a method for operating and steering a fluid hammer while drilling a bore-hole by coupling the fluid hammer to a pipe-in-pipe bent steering member including an inner pipe member and an outer pipe member. The inner pipe member can be rotated independently from the outer pipe member. The outer pipe member of the bent steering member may be positioned and held stationary by means of the outer pipe members of the drill string while the inner pipe member is rotated
A variety of advantages of the invention will be set forth in part in the description that follows, and in part will be apparent from the description, or may be learned by practicing the invention. It is to be understood that both the foregoing general description and the following detailed description are explanatory only and are not restrictive of the invention as claimed.